Modern technology utilizes positive-type resist materials for lithographically delineating patterns onto a substrate so that the patterns can be subsequently etched or otherwise defined into the substrate material. The resist material is deposited as a film and the desired pattern is defined by exposing the resist film to energetic radiation. Thereafter the exposed regions are subject to a dissolution by a suitable developer liquid. After the pattern has been thus defined in the substrate the resist material must be completely removed from the substrate to avoid adversely affecting or hindering subsequent operations or processing steps.
It is necessary to such a photolithographic process that the photoresist material, following pattern delineation, be evenly and completely removed from all unexposed areas so as to permit further lithographic operations. Even the partial remains of a resist in an area to be further patterned is undesirable. Also, undesired resist residues between patterned lines can have deleterious effects on subsequent processes, such as metallization, or cause undesirable surface states and charges.
Heretofore the resist materials have been removed by stripping agents containing one or more of the following: halogenated hydrocarbons, for example, methylene chloride or tetrachloroethylene; amines and their derivatives such as dimethylformamide, N-methyl-2-pyrrolidone, diethanolamine and triethanolamine; glycol ethers such as ethylene glycol monoethyl ether, 2-butoxyethanol, 2-(2-butoxyethoxy)ethanol, and the acetates thereof; ketones such as methyl ethyl ketone, acetone, methyl isobutyl ketone and cyclohexanone, as well as such materials as dioxane, sodium phenolate, isopropyl alcohol, sulfuric acid/nitric acid mixtures, persulfuric acid mixtures such as Caro's acid and sulfuric acid/ammonium persulfate, and mixtures of caustic and phenol derivatives as well as various other materials.
However, there are various and numerous drawbacks and disadvantages with these various materials. Among the one or more drawbacks and disadvantages found in the use of each such stripping agents there may be mentioned the following: undesirable flammability, volatility, odor and toxicity; incomplete removal of all resist film; effectiveness only on certain resist films; attack of components other than the resist material, such as attack of metal substrates by the stripping agent; safely in handling and disposal of the stripper; and the undesired necessity for use at specified elevated temperatures when selected resists are being stripped. Furthermore, the limited stripping capabilities of the stripping agents is a very decided drawback. Additionally, many such strippers are not sufficiently effective against resist materials that are subject to a severe post-baking operation thereby limiting their usefulness. In some of the strippers the presence of water is extremely detrimental. Additionally, for those stripping applications requiring inertness of the agent to metal substrates, toxicity during handling and difficulty of disposal are primary drawbacks.